In normal operation, electric starter motors for diesel engines intermittently draw a substantial quantity of power for brief periods. The lead-acid batteries designed to meet the relatively brief, high power draw characteristic of these electric starter motors do not exhibit good deep and high cycle characteristics. Repeated deep discharge of such “starter” or “high output” batteries can greatly shorten the useful life of the batteries. Starter batteries last substantially longer if the batteries are kept fully charged and high cycling and deep discharge of the batteries is avoided.
Supplying power for cold cranking of the engine is not the only power demand present on vehicles when the engine is off. Trucks used for long haul shipping and equipped with sleeper compartments may rely on battery supplied electrical power during periods when the vehicle's engine is not running and the alternator is not available to supply the electricity used for communication equipment, radios, lights, microwave ovens, televisions, computers, etc. Split or “dual” battery systems have been used where multiple batteries are installed on a vehicle with some of the batteries reserved for starting the vehicle and other batteries being used to supply electricity to electrical loads when the engine is not running. Canadian Patent Application No. 2 538 646 teaches a representative split battery system for a truck. There it was suggested that battery types be differentiated between starter batteries and high/deep cycle batteries tolerant of deep discharge to be used for longer duration, relatively steady loads.
Contemporary regulations relating to commercial motor vehicle drivers provide that drivers are to take at least 8 consecutive hours in the sleeper berth, plus 2 consecutive hours either in the sleeper berth, off duty, or any combination of the two. This differs from prior regimes where drivers using a sleeper berth were to take 10 hours off duty, but could split sleeper berth time into two periods provided neither was less than 2 hours. Long sleeper birth time and increasingly accessible DC power accessories appear to have resulted in an increase in vehicle electrical loads when the engine is not running and deeper discharging of vehicle batteries. There is also evidence of shorter duration runs of trucks with a consequential diminishment of full recharging of the starter batteries. These factors contribute to batteries not being fully charged and to high parasitic loads on the batteries pushing the batteries into high cycling and deep discharge conditions with consequential shortening of battery life.